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991.
A water quality model for the Patuxent estuary: Current conditions and predictions under changing land-use scenarios 总被引:1,自引:0,他引:1
A water quality model was developed for the Patuxent estuary using the modeling framework CE-QUAL-W2 (called W2) to address the impact of current and projected land-use changes (stress) on the water quality. The W2 code, supported by the Army Corps of Engineers Waterways Experiment Station, is a two-dimensional (longitudinalvertical) model designed for hydrodynamic and water quality simulations of reservoirs and estuaries. The code was configured for the Patuxent estuary using a finite-difference grid for the water column. Also incorporated into the model calculations are flow and nutrient load results from a watershed model. The integrated model was calibrated with data of 1 yr from 1997 to 1998 by matching results with measured temperature, dissolved oxygen, chlorophylla, and nutrient levels in the water column. The calibrated model was used to predict the water quality effects of different watershed land-use scenarios. Model projection results suggest that reductions of nutrient loads would lead to improvement of anoxic conditions in the bottom waters of the lower Patuxent estuary. 相似文献
992.
Dissolved oxygen (DO) and nitrate concentrations of groundwater from a total of 191 new monitoring wells, with a maximum depth up to 300 m, in the Choshui fan delta of Taiwan were measured to delineate the regional patterns of the two components. Unconfined aquifers of the proximal part of the fan delta contain 1~7 mg/l of DO, and a 250-m deep well still has an unusual value of 1.83 mg/l. DO concentrations decrease downgradient along flow paths to below detection limit (0.01 mg/l) in shallow confined aquifers during the last 40 years, possibly due to oxidation of organic matters in sediments. A plume of high nitrate-N concentrations (0.5–17 mg/l) originating from the proximal part of the fan delta has been developing, possibly since 1956, due to agricultural fertilizers. From 1997 to 2001, the concentration has increased at a rate of ca. 0.28 mg/l per year. 相似文献
993.
Marc?Hesse Timothy?L.?GroveEmail author 《Contributions to Mineralogy and Petrology》2003,146(1):10-27
We have investigated the near liquidus phase relations of a primitive absarokite from the Mascota region in western Mexico. Sample M.102 contains ~11.6 wt% MgO, Mg#=0.73 and the lava contains Fo90 olivine phenocrysts, indicating near equilibrium with the mantle. High-pressure experiments on a synthetic analogue of the absarokite composition containing low and high H2O abundances of (~2 and ~5 wt%, respectively) were performed in a piston cylinder apparatus over the pressure range of 1.2 to 2.0 GPa. The composition containing ~2 wt% H2O is multiply saturated with olivine and orthopyroxene at 1.6 GPa and 1,400 °C. At the same pressure, clinopyroxene appears 30 °C below the liquidus. At an H2O content of ~5 wt% the multiple saturation with olivine and orthopyroxene occurs at 1.7 GPa and 1,300 °C. Assuming a batch-melting process, we suggest that the primitive absarokite was segregated from a depleted lherzolite or harzburgite residue at ~50 km, placing the depth of origin well within the mantle wedge beneath the Jalisco Block. A low degree (<5 %wt%) batch-melt of an original metasomatized depleted lherzolite or harzburgite source would contain the observed trace element abundances found in M.102. The liquidus phase relations are not consistent with the presence of non-peridotitic veins at the depth of last equilibration. Therefore, we propose that the Mascota absarokites segregated at an apparent melt fraction of less than 5% from a depleted peridotitic source. Melting first began at a greater depth as a small degree H2O- and trace element- rich melt of a metasomatized peridotite that ascended into the overlying wedge and re-equilibrated with shallower, hotter mantle.Editorial responsibility: J. Hoefs 相似文献
994.
Stephen?MoyseyEmail author Stanley?N.?Davis Marek?Zreda L.?DeWayne?Cecil 《Hydrogeology Journal》2003,11(6):615-627
The natural distribution of 36Cl/Cl in groundwater across the continental United States has recently been reported by Davis et al. (2003). In this paper, the large-scale processes and atmospheric sources of 36Cl and chloride responsible for controlling the observed 36Cl/Cl distribution are discussed.The dominant process that affects 36Cl/Cl in meteoric groundwater at the continental scale is the fallout of stable chloride from the atmosphere, which is mainly derived from oceanic sources. Atmospheric circulation transports marine chloride to the continental interior, where distance from the coast, topography, and wind patterns define the chloride distribution. The only major deviation from this pattern is observed in northern Utah and southern Idaho where it is inferred that a continental source of chloride exists in the Bonneville Salt Flats, Utah.In contrast to previous studies, the atmospheric flux of 36Cl to the land surface was found to be approximately constant over the United States, without a strong correlation between local 36Cl fallout and annual precipitation. However, the correlation between these variables was significantly improved (R
2=0.15 to R
2=0.55) when data from the southeastern USA, which presumably have lower than average atmospheric 36Cl concentrations, were excluded. The total mean flux of 36Cl over the continental United States and total global mean flux of 36Cl are calculated to be 30.5±7.0 and 19.6±4.5 atoms m–2 s–1, respectively.The 36Cl/Cl distribution calculated by Bentley et al. (1986) underestimates the magnitude and variability observed for the measured 36Cl/Cl distribution across the continental United States. The model proposed by Hainsworth (1994) provides the best overall fit to the observed 36Cl/Cl distribution in this study. A process-oriented model by Phillips (2000) generally overestimates 36Cl/Cl in most parts of the country and has several significant local departures from the empirical data.
Resumen Davis et al. (2003) han informado de la distribución natural de la proporción 36Cl/Cl en las aguas subterráneas de la parte continental de los Estados Unidos de América [EUA]. En este artículo, se discute cuáles son los procesos a gran escala y las fuentes atmosféricas del 36Cl y del cloruro que dan lugar a la distribución observada de 36Cl/Cl.El proceso dominante que afecta a la relación 36Cl/Cl en las aguas subterráneas de origen meteórico a escala continental es el aporte de cloruro estable desde la atmósfera, que procede principalmente de los océanos. La circulación atmosférica transporta el cloruro marino hacia el interior, donde la distancia a la costa, topografía y corrientes del viento definen la distribución del cloruro. La única desviación principal de este esquema tiene lugar al norte de Utah y en el sur de Idaho, donde se deduce que existe una fuente continental de cloruro en los Rellanos Salados de Bonneville (Salt Flats).En contraste con estudios previos (Knies et al. 1994; Phillips 2000), se ha descubierto que el flujo atmosférico de 36Cl hacia la superficie terrestre es aproximadamente constante en todos los estados, sin deducirse una correlación fuerte entre el aporte de 36Cl y la precipitación anual. Sin embargo, la correlación entre estas variables se ve mejorada de forma significativa, con coeficientes de regresión comprendidos entre 0,15 y 0,55, cuando se excluyen los datos recogidos en el sudeste de los EUA, que tienen concentraciones de 36Cl atmosférico presuntamente inferiores a la media. El flujo medio total de 36Cl calculado en la zona continental de los Estados Unidos vale 30,5±7,0 átomos por metro cuadrado y segundo, mientras que el flujo total global de 36Cl es de 19,6±4,5 átomos por metro cuadrado y segundo.La distribución de 36Cl/Cl calculada por Bentley et al. (1986) infravalora la magnitud y variabilidad observada en los valores medidos a lo largo de los Estados Unidos. El modelo propuesto por Hainsworth (1994) proporciona el mejor ajuste conjunto a la distribución observada de 36Cl/Cl en este estudio. El modelo orientado a procesos de Phillips (2000) sobreestima por lo general la distribución de 36Cl/Cl en la mayoría del país y difiere significativamente de algunos valores locales empíricos.
Résumé La distribution naturelle du rapport 36Cl/Cl dans les eaux souterraines des États-Unis a été récemment présentée par Davis et al. (2003). Dans ce travail, les processus à grande échelle et les sources atmosphériques de 36Cl et de chlorure responsables du contrôle de la distribution observée du rapport 36Cl/Cl sont discutés. Le processus dominant qui affecte le rapport 36Cl/Cl dans les eaux souterraines dorigine météorique à léchelle continentale est lapport atmosphérique de chlorure stable, qui provient pour lessentiel de sources océaniques. La circulation atmosphérique transporte des chlorures marins vers lintérieur des continents, où la distribution de chlorure est définie par la distance à la côte, la topographie et les régimes des vents. La seule exception majeure à ce schéma est observée dans le nord de lUtah et le sud de lIdaho où lon suppose quil existe une source continentale de chlorure dans les bas-fonds salés de Bonneville. Au contraire de précédentes études (Knies et al. 1994; Phillips 2000), on trouve que le flux atmosphérique de 36Cl vers le sol est approximativement constant sur lensemble des États-Unis, sans forte corrélation entre la retombée locale de 36Cl et les précipitations annuelles. Cependant, la corrélation entre ces variables devient significative (R 2=0.15 à 0.55) lorsquon supprime les données du sud-est des États-Unis, dont on pense quelles présentent des concentrations en 36Cl atmosphérique inférieures à la moyenne. Le flux total moyen de 36Cl sur les États-Unis continentaux et le flux moyen global de 36Cl sont respectivement évalués à 30.5 ± 7.0 et 19.6 ± 4.5 atomes.m–2.s–1. La distribution du rapport 36Cl/Cl calculée par Bentley et al. (1986) sous-estime lordre de grandeur et la variabilité observés pour la distribution mesurée du rapport 36Cl/Cl sur les États-Unis continentaux. Le modèle proposé par Hainsworth (1994) fournit le meilleur ajustement densemble à la distribution du rapport 36Cl/Cl observée dans cette étude. Un modèle orienté vers les processus proposé par Phillips (2000) surestime dans lensemble le rapport 36Cl/Cl dans la plupart des régions du pays et présente plusieurs désaccords locaux avec les données empiriques.相似文献
995.
Elisabetta?Brizi Sabrina?NazzareniEmail author Francesco?Princivalle Pier?Francesco?Zanazzi 《Contributions to Mineralogy and Petrology》2003,145(5):578-584
Optically homogeneous augite xenocrysts, closely associated with spinel–peridotite nodules, occur in alkali basalts from Hannuoba (Hebei province, China). They were studied by electron and X-ray diffraction to define the occurrence and significance of pigeonite exsolution microtextures. Sub-calcic augite (Wo34) exsolved into En62–62Fs25–21Wo13–17 pigeonite and En46–45Fs14–14Wo40–42 augite, as revealed by TEM through diffuse coarser (001) lamellae (100–300 Å) and only incipient (100) thinner ones (<70 Å). C2/c augite and P21/c pigeonite lattices, measured by CCD-XRD, relate through a(Aug)?a(Pgt), b(Aug)?b(Pgt), c(Aug)≠c(Pgt) [5.278(1) vs 5.189(1)Å] and β(Aug)≠β(Pgt) [106.55(1) vs 108.55(2)°]. Cell and site volumes strongly support the hypothesis that the augite xenocrysts crystallised at mantle depth from alkaline melts. After the augite xenocrysts entered the magma, (001) lamellae first formed by spinodal decomposition at a Tmin of about 1,100 °C, and coarsened during very rapid transport to the surface; in a later phase, possibly on cooling, incipient (100) lamellae then formed. 相似文献
996.
A Sr isotope study on fluorite and siderite from post-orogenic mineral veins in the eastern Harz Mountains,Germany 总被引:2,自引:0,他引:2
Rb–Sr isotope data for siderite and fluorite from sediment-hosted epithermal mineral veins in the eastern Harz Mountains (Germany)
are presented. Several fluorite and siderite-bearing paragenetic stages have been proposed for these veins, with the most
important mineralization being related to a quartz–sulfide and a subsequent calcite–fluorite–quartz stage, which occurred
at 226±1 and 209±2 Ma, respectively. Our Rb–Sr data do not permit the identification of distinct generations of siderite and
fluorite, but rather reveal straight internal mixing relations, reflecting mixing of fluids or differential fluid–rock interaction
processes. This indicates merely two significant phases of mineral deposition related to the quartz–sulfide and calcite–fluorite–quartz
stages. It is shown that the Paleozoic sedimentary host rocks of the veins are the most likely source for the siderite Sr,
whereas fluorite displays a two-component mixture between sedimentary Sr and radiogenic Sr derived from locally occurring
Permian metavolcanic rocks.
Editorial handling: B. Lehmann 相似文献
997.
998.
999.
本文以模糊子集论为指导,在迪戴的DCM法的基础上提出了动态聚类-模糊模式识别方法。实际上,它是一种新的模糊聚类的方法。该方法以DCM法的动态聚类部分做为原始数据变换的手段,而将迪戴的强模式概念推广为模糊模式,将强模式识别推广为模糊模式识别。此外,还提出了模糊模式间联系度的概念,从而解决了类间联系、类内典型个体、类间过渡个体、个体对各类的隶属程度以及内部有某种演化趋势的类别的划分等问题。文章还给出了该方法的数学模型和算法概要。最后,通过一个在地质学中的应用实例,说明了该方法的应用效果。 相似文献
1000.
地下热水是热储形式之一,目前应在“能得用地热储量”(一般指2000m以内)范围内寻找。成都平原地下热水属“暂难利用的地热储量”。在众多的地热论证或成果中较少涉及地热资源基本类型对地热开发是不利的。花水湾泉有许多有益的启示,龙门山山前地带值行重视。地热地常规开发程序是必要的应保持它的严肃性。 相似文献